[mantap]

In mathematics the word used for these kinds of problems is "inaccessible", e.g. Reimann Hypothesis or (previously) Fermat'a Last Theorem. I don't know if Carmack's chances are as good as Wiles' were but certainly better than the average joe. It's also the case that AI is a substantially younger field (arguably it was only possible to correctly evaluate ideas since powerful GPUs were released this decade) and so the difficulty of open problems including AGI is not yet known.